Reciprocal latching phase modulator for microwave frequencies

This paper describes the design and operation of a new type of latching (or digital) phase modulator in standard rectangular waveguide. This new device uses the square-loop magnetic properties of toroidal ferrite materials to obtain digital increments of reciprocal phase shift. By latching or switching the magnetization of this square-loop ferrite material from a zero-field value to either one of its two remanent states, a corresponding phase shift of the microwave energy is produced. The electrical characteristics of these latching-type phase modulators, typical of those obtained for early test models designed for band, include reciprocal phase shifts of approximately 180°/in, insertion loss less than 0.8 dB, input VSWR no greater than 1.5, amplitude modulation less than ±;0.2 dB and an operating bandwidth of five percent. They can be switched to either of two stable states in approximately 1 μs with little switching energy. They are also capable of digital operation with noncritical driver current pulses, requiring no holding power to maintain phase in either state.